Optical surfaces

Optical surfaces

Interfaces between different optical media at which light is refracted or reflected. From a physical point of view, the basic elements of an optical system are such things as lenses and mirrors. However, from a conceptual point of view, the basic elements of an optical system are the refracting or reflecting surfaces of such components. Surfaces are the basic elements of an optical system because they are the elements that affect the light passing through the system. Every wavefront has its curvature changed on passing through each surface so that the final set of wavefronts in the image space may converge on the appropriate image points. Also, the aberrations of the system depend on each surface, the total aberrations of the system being the sum of the aberrations generated at the individual surfaces. See Aberration (optics), Reflection of electromagnetic radiation, Refraction of waves

Optical systems are designed by ray tracing, and refraction at an optical surface separating two media of different refractive index is the fundamental operation in the process. The transfer between two surfaces is along a straight line if, as is usually the case, the optical media are homogeneous. The refraction of the ray at a surface results in a change in the direction of the ray. This change is governed by Snell's law.

The vast majority of optical surfaces are spherical in form. This is so primarily because spherical surfaces are much easier to generate than nonspherical, or aspheric, surfaces. Moreover, lens systems seldom need aspherics because the aberrations can be controlled by changing the shape of the component lenses without changing their function in the system, apart from modifying the aberrations. Also, many lens components can be included in a lens system in order to control the aberrations. See Lens (optics)

On the other hand, mirror systems usually require aspheric surfaces. Unlike lenses, where the shape can be changed to modify the aberrations, mirrors cannot be changed except by introducing aspheric surfaces. Mirror systems are further constrained by the fact that only a few mirrors, usually two, are used in a system because each successive mirror occludes part of the beam going to the mirror preceding it. See Mirror optics

The most common form of rotationally symmetric surface is the conic of revolution. The departure of conic surfaces from spherical form is shown in the illustration. The classical virtue of the conics of revolution for mirrors is the fact that light from a point located at one focus of the conic is perfectly imaged at the other focus. If these conic foci are located on the axis of revolution, the mirror is free of spherical aberration for such conjugate points.

Conics of revolutionenlarge picture
Conics of revolution
References in periodicals archive ?
Freeform optical surfaces provide many advantages over conventional optics for meeting complex illumination requirements, such as precise light control, innovative styling, compact system dimensions and energy efficiency.
Additionally, Grundig is to showcase its new water-repellent, Rain-Wash coating for the optical surfaces of domes.
Durham University hosts the project and principle investigator Professor Ray Sharples, of the Department of Physics, who is also the Director of the Centre for Advanced Instrumentation, said: "One of the unique features of KMOS is the system of diamond-machined image slicers, produced by Durham Precision Optics, which consists of over a thousand gold-coated optical surfaces each manufactured with a precision of a few billionths of a metre.
Among specific topics are calculating the effective ground depth of cut by means of a grinding process model, comparing picosecond and femtosecond laser ablation for the surface engraving of metals and semiconductors, pulsed processes when cutting heat-resistant alloys, reactive atom plasma for the rapid figure correction of optical surfaces, and the thrust force of printed circuit board drilling.
The mirrors were rinsed thoroughly with distilled water before wads of cotton wool soaked in a weak sodium lauryl sulphate solution were used to drag-wipe the optical surfaces.
We would also like to hear from anyone who may be able to help with the acquisition of a suitable 2-mirror type coelostat delivering a beam between 4 and 12 inches clear aperture: it doesn't matter how old and well-worn, as long as the optical surfaces are undamaged and the mechanicals serviceable.
The lens is constructed with two flexible membranes on the optical surfaces, held in place by a solid surround.
They are waterproof to 16'6" and nitrogen filling prevents fogging of internal optical surfaces.
At synchrotron laboratories the beamlines are often equipped with devices to enable cleaning of the optical surfaces with oxygen plasmas (2).
Beginning with a section on light propagation, which tackles the difficult question of defining light, chapters progress to cover reflections and refractions at optical surfaces, image formation, mirrors and prisms, curved optical surfaces, thin lenses, thick lenses, mirrors, optical apertures, paraxial ray tracing, aberrations in optical systems and real ray tracing.
Our process uses MRF to polish optical surfaces to extreme precision," Steve Hogan, QED alliance manager, said, "where the form error on a surface of 8" in diameter is typically less than one- to two-millionths of an inch.

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